The present disclosure relates generally to the art of induction heating. More specifically, it relates to using a moveable induction heating head assembly, a temperature sensor assembly, and a travel sensor assembly.
Induction heating may be used to pre-heat metal before welding or post-heat the metal after welding. It is well known to weld pieces of steel (or other material) together. For example, pipes are often formed by taking a flat piece of steel and rolling the steel. A longitudinal weld is then made along the ends of the rolled steel, thus forming a section of pipe. A pipeline may be formed by circumferential welding adjacent sections of pipe together. Other applications of welding steel (or other material) include ship building, railroad yards, tanker trucks, or other higher strength alloy welding.
When welding steel (or other material), it is generally desirable to pre-heat the workpiece along the weld path. Pre-heating is used to raise the temperature of the workpiece along the weld path because the filler metal binds to the workpiece better when the weld path is pre-heated, particularly when high-alloy steel is being welded. Without pre-heating, there is a greater likelihood that the filler metal will not properly bind with the workpiece, and a crack may form, for example. Generally, the steel is preheated to about 300° F. prior to welding.
Conventional pre-heating techniques use “rose buds” (gas-fired flame torches), resistance “chicklets”, or induction heating blankets to pre-heat the steel. For example, rosebuds may be placed along the weld path, typically one rosebud on each side of the weld path, or one covering both sides of the weld path, for every 3 to 6 feet. The rosebuds are left in place a relatively long period of time (e.g., up to two hours for 3″ thick steel). After the weld path has been pre-heated, the rose buds are removed and the weld is performed before the weld path cools.
Induction heating blankets are used to pre-heat a weld by wrapping an induction blanket (e.g., an induction cable inside a thermally safe material), and inducing current in the workpiece. Induction heating can be a fast and reliable way to pre-heat, particularly on stationary workpieces. However, induction blankets have certain challenges when used with moving workpieces, and some pipe welding applications have a fixed position welder with a pipe that moves or rotates past the weld location. Liquid-cooled cables offer flexibility in coil configurations, but have similar issues with rotating pipes rolling up cables or wearing through the insulation.
Other methods of pre-heating a weld path include placing the entire workpiece in an oven (which takes as long as using a rosebud), induction heating, or resistance heating wires. When pre-heating with these conventional techniques, the heating device is placed at one location on the weld path until that location is heated. Then, the weld is performed and the heating device is moved.
Often, these conventional approaches for pre-heating workpieces use various methods (e.g., temperature sensitive crayons) for monitoring the temperature of the workpieces, but do not have temperature feedback for controlling the power source. Accordingly, a system for pre-heating a weld path and for incorporating temperature and/or travel feedback into the control of the pre-heating is desirable.